The present invention relates to an apparatus and method for detecting the inspirations of a patient.
In monitoring a patient, it is desirable to detect and measure the rate of inspiration of the patient, inspiration being the act of drawing air into the lungs. Prior art devices do this by establishing a baseline level for the time varying bipolar respiration signal which level falls between (usually midway between) the peak to peak variations of the respiration signal. A trigger level, a predetermined amount above the baseline level, is established and selected ones of the positive crossovers are chosen as inspiration events.
Usually prior art devices include a cardiovascular detector for detecting the presence of cardiovascular artifact (CVA, a low level time varying signal which is created by the pumping action of the heart into the thoracic-cavity) and inhibiting the output of inspiration trigger signals when it is suspected that the inspiration detector is detecting CVA and not inspiration.
Also, prior art devices will only generate an inspiration signal if the respiration signal remains positive for a predetermined amount of time after a positive crossover of a trigger level.
Sometimes due to patient movement, for example, there will be a sudden shift up or down of the dc level of the respiration waveform which will cause the inspiration detector to lose track of the signal and miss valid inspiration events. Prior art devices are not equipped to detect baseline shifts in a timely manner, e.g. within a respiration cycle or two of the shift. It is desirable in adults and particularly in neonates to react quickly to sudden baseline shifts in the respiration signal, and to be able to accommodate both adult and neonate inspiration detection characteristics like CVA, qualifier time and baseline and trigger level calculations in the same apparatus.